U.S. Department of the Interior

U.S. Geological Survey

Pamphlet to accompany 

Scientific Investigations Map 3278

Prepared in cooperation with City of Frankfort, Kentucky, Office of Emergency Management

Flood-Inundation Maps for a 6.5-Mile Reach of the 

Kentucky River at Frankfort, Kentucky
Cover

Background image: Flood inundation area at stage 52.

Small photos: Flood views in Frankfort, Kentucky. 

Photo courtesy of Cloyd Stratton and Steven P. Cohen.
Flood-Inundation Maps for a 6.5-Mile Reach 

of the Kentucky River at Frankfort, Kentucky

By Jeremiah G. Lant

Prepared in cooperation with City of Frankfort, Kentucky, 

Office of Emergency Management

Pamphlet to accompany 

Scientific Investigations Map 3278

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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U.S. Government.

Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials 

as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner.

Suggested citation:

Lant, J.G., 2013, Flood-inundation maps for a 6.5-mile reach of the Kentucky River at Frankfort, Kentucky: U.S. 

Geological Survey Scientific Investigations Map 3278, 26 sheets, 10-p. pamphlet, http://dx.doi.org/10.3133/sim3278.

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3278
iii

Contents

Acknowledgments........................................................................................................................................vi

Abstract...........................................................................................................................................................1

Introduction ....................................................................................................................................................1

Purpose and Scope ..............................................................................................................................2

Study Area Description........................................................................................................................2

Previous Studies ..................................................................................................................................2

Constructing Water-Surface Profiles.........................................................................................................4

Hydrologic and Steady-Flow Data .....................................................................................................4

Topographic/Bathymetric Data ..........................................................................................................4

Energy-Loss Factors.............................................................................................................................5

Model Calibration and Performance .................................................................................................5

Development of Water-Surface Profiles...........................................................................................5

Inundation Mapping ......................................................................................................................................9

Kentucky River, Kentucky, Flood-Inundation Maps on the Internet.............................................9

Disclaimer for Flood-Inundation Maps .............................................................................................9

Uncertainties and Limitations for Use of Flood-Inundation Maps ...............................................9

Summary........................................................................................................................................................10

References Cited..........................................................................................................................................10

Glossary.........................................................................................................................................................10

Sheets

Sheets and additional materials are available online at http://dx.doi.org/10.3133/sim3278/.

1–26. Estimated flood-inundation maps for the Kentucky River from reach near 

Interstate 64 to reach near Lock 4 referenced to USGS streamgage Kentucky River 

at Lock 4 at Frankfort, Kentucky (sta. no. 03287500) for stream stages of:

1. 27 feet and an elevation of 488.58 feet.

2. 28 feet and an elevation of 489.58 feet.

3. 29 feet and an elevation of 490.58 feet.

4. 30 feet and an elevation of 491.58 feet.

5. 31 feet and an elevation of 492.58 feet.

6. 32 feet and an elevation of 493.58 feet.

7. 33 feet and an elevation of 494.58 feet.

8. 34 feet and an elevation of 495.58 feet.

9. 35 feet and an elevation of 496.58 feet.

10. 36 feet and an elevation of 497.58 feet.

11. 37 feet and an elevation of 498.58 feet.

12. 38 feet and an elevation of 499.58 feet.

13. 39 feet and an elevation of 500.58 feet.

14. 40 feet and an elevation of 501.58 feet.

15. 41 feet and an elevation of 502.58 feet.
iv

Sheets–continued

16. 42 feet and an elevation of 503.58 feet.

17. 43 feet and an elevation of 504.58 feet.

18. 44 feet and an elevation of 505.58 feet.

19. 45 feet and an elevation of 506.58 feet.

20. 46 feet and an elevation of 507.58 feet.

21. 47 feet and an elevation of 508.58 feet.

22. 48 feet and an elevation of 509.58 feet.

23. 49 feet and an elevation of 510.58 feet.

24. 50 feet and an elevation of 511.58 feet.

25. 51 feet and an elevation of 512.58 feet.

26. 52 feet and an elevation of 513.58 feet. 

Figures

1. Map showing location of study reach for the Kentucky River at Frankfort, 

Kentucky, and location of USGS streamgages........................................................................3

2. Comparison of hydraulic-model output and stage-discharge rating at Kentucky 

River at Lock 4 at Frankfort, Kentucky.......................................................................................8

3. Comparison of hydraulic-model output and high-water-mark elevations for a 

major flood event on May 5, 2010, Kentucky River, Kentucky ...............................................8

Tables

1. USGS streamgage information for study basin, Kentucky River, Kentucky........................5

2. Comparison of hydraulic-model output and stage-discharge rating at Kentucky 

River at Lock 4 at Frankfort, Kentucky.......................................................................................6

3. Comparison of hydraulic-model output and high water mark elevations for a 

major flood event on May 5, 2010, Kentucky River, Kentucky ...............................................6

4. Stages (elevations), in feet, with corresponding discharge estimates at USGS 

station 03287500 ............................................................................................................................7
v

Multiply By To obtain

Length

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2) 2.590 square kilometer (km2)

Flow rate

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

Hydraulic gradient

foot per mile (ft/mi) 0.1894 meter per kilometer (m/km)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 

(NAD 83).

Conversion Factors

Inch/Pound to SI
vi

Acknowledgments

The author wishes to thank the local, State, and Federal agencies that have cooperated in and 

(or) funded for the operation and maintenance of the streamgage used for this study, especially 

the City of Frankfort Office of Emergency Management. Special thanks are given to Deron 

Rambo, Director of Emergency Management for the City of Frankfort at the Office of Emergency 

Management, for his cooperation in this study and to the National Weather Service for their 

continued support of the USGS flood-inundation mapping initiative.
Flood-Inundation Maps for a 6.5-Mile Reach of the 

Kentucky River at Frankfort, Kentucky

By Jeremiah G. Lant 

Abstract

Digital flood-inundation maps for a 6.5-mile reach of 

Kentucky River at Frankfort, Kentucky, were created by 

the U.S. Geological Survey (USGS) in cooperation with the 

City of Frankfort Office of Emergency Management. The 

inundation maps, which can be accessed through the USGS 

Flood Inundation Mapping Science Web site at http://water.

usgs.gov/osw/flood_inundation/, depict estimates of the areal 

extent and depth of flooding corresponding to selected water 

levels (stages) at the USGS streamgage Kentucky River at 

Lock 4 at Frankfort, Kentucky (station no. 03287500). Current conditions for the USGS streamgage may be obtained 

online at the USGS National Water Information System 

site (http://waterdata.usgs.gov/nwis/inventory?agency_

code=USGS&site_no=03287500). In addition, the information 

has been provided to the National Weather Service (NWS) for 

incorporation into their Advanced Hydrologic Prediction Service (AHPS) flood warning system (http:/water.weather.gov/

ahps/). The NWS forecasts flood hydrographs at many places 

that are often colocated at USGS streamgages. The forecasted 

peak-stage information, also available on the Internet, may be 

used in conjunction with the maps developed in this study to 

show predicted areas of flood inundation. 

In this study, flood profiles were computed for the Kentucky River reach by using HEC–RAS, a one-dimensional 

step-backwater model developed by the U.S. Army Corps of 

Engineers. The hydraulic model was calibrated by using the 

most current (2013) stage-discharge relation for the Kentucky 

River at Lock 4 at Frankfort, Kentucky, in combination with 

streamgage and high-water-mark measurements collected for a 

flood event in May 2010. The calibrated model was then used 

to calculate 26 water-surface profiles for a sequence of flood 

stages, at 1-foot intervals, referenced to the streamgage datum 

and ranging from a stage near bankfull to the elevation that 

breached the levees protecting the City of Frankfort. To delineate the flooded area at each interval flood stage, the simulated 

water-surface profiles were combined with a digital elevation 

model (DEM) of the study area by using geographic information system software. The DEM consisted of bare-earth 

elevations within the study area and was derived from a Light 

Detection And Ranging (LiDAR) dataset having a 5.0-foot 

horizontal resolution and an accuracy of 0.229 foot. 

 The availability of these maps, along with Internet information regarding current stages from USGS streamgages and 

forecasted stages from the NWS, provides emergency management personnel and local residents with critical information 

for flood response activities such as evacuations, road closures, and postflood recovery efforts.

Introduction 

The City of Frankfort, Kentucky, is an urban community 

with an estimated population of 27,590 (U.S. Census Bureau, 

2012). Frankfort, the capital of Kentucky, is located within a 

sharp bend of the Kentucky River. The Kentucky River flows 

through the heart of Frankfort, splitting the city into a northern 

and southern part. Frankfort’s location and low-lying flood 

plains make the city susceptible to flooding. According to the 

flood categories established by the National Weather Service, 

the City of Frankfort has experienced approximately 58 flood 

events within the last 100 years, most notably in 1978. 

Prior to this study, Frankfort officials relied on several 

information sources (all of which are available on the Internet) 

to make decisions on how to best alert the public and mitigate 

flood damages. One source is the September 28, 2007, Federal 

Emergency Management Agency (FEMA) Flood Insurance 

Study (FIS) for Franklin County and Incorporated Areas 

(Federal Emergency Management Agency, 2007). A second 

source of information consists of a USGS streamgage that lies 

within the city limits of Frankfort: Kentucky River at Lock 4 

at Frankfort, Kentucky (station no. 03287500), from which 

current and historical water levels (stage) can be obtained. A 
2 Flood-Inundation Maps for a 6.5-Mile Reach of the Kentucky River at Frankfort, Kentucky

third source is the National Weather Service forecast of peak 

stage at the USGS Kentucky River Lock 4 streamgage (station 

no. 03287500) through the Advanced Hydrologic Prediction Service (AHPS) Web site (NWS forecast point FFTK2). 

Although current USGS stage and NWS forecasted stage 

information is particularly useful for residents in the immediate vicinity of a streamgage, it is of limited use to residents 

farther upstream or downstream because the water-surface 

elevation is not constant along the entire stream channel. Also, 

FEMA, State emergency management mitigation teams, and 

property owners typically lack information related to water 

depth at locations other than near a USGS streamgage or an 

NWS flood-forecast point. 

Purpose and Scope

The purpose of this report is to (1) describe the development of a series of estimated flood-inundation maps for a 6.5-

mile reach of the Kentucky River near Frankfort, Kentucky, 

and (2) provide the City of Frankfort and the public with a 

library of flood-inundation maps that correspond to water levels referenced to the water-surface elevation and gage heights 

at the USGS streamgage at Kentucky River Lock 4 at Frankfort, Kentucky (station no. 03287500). The flood-inundation 

maps and other flood information are made available on the 

USGS Flood Inundation Mapping Science Web site at 

http://water.usgs.gov/osw/flood_inundation/. Internet users can 

select estimated inundation maps that correspond to current 

stages at the USGS streamgage, the NWS forecasted peak 

stage, or other desired stream stages.

The scope of the study was limited to the Kentucky River 

reach bounded by Interstate 64, approximately 5 miles (mi) 

south of Frankfort, and an area approximately 1 mi north of 

Lock 4 (fig. 1). To develop flood-inundation maps, a hydraulic 

model of the Kentucky River reach was built to provide watersurface profiles for various flood stages. 

Study Area Description

The Kentucky River is a tributary of the Ohio River. The 

headwaters originate in the Cumberland Mountains of southeast Kentucky, and the river flows generally northwestward for 

approximately 250 mi through the heart of Kentucky before 

entering the Ohio River. The reach studied is in north-central 

Kentucky in what is locally called the Bluegrass Region. The 

drainage area ranges from 5,411 square miles (mi2) at station 

03287500 to 6,950 mi2 at the confluence of the Ohio River. No 

major tributary to the Kentucky River joins the main stem as 

it flows through Frankfort, but there are a few minor tributaries; among these is Benson Creek, which joins the main stem 

south of Frankfort and approximately 300 feet (ft) downstream 

of station 03287500. The basin terrain changes gradually from 

steep to rolling hills adjacent to the city to low-lying and flat 

areas within the city. The study reach is approximately 6.5 mi 

long, has an average top-of-bank channel width of about 400 

ft, and has an average channel slope of 1 foot per mile. The 

basin is still undergoing suburban and urban development; 

population increased 1.2 percent (from 27,269 to 27,590) 

between 2010 and 2012 (U.S. Census Bureau, 2012). The 

main channel within the study reach has six major road crossings or other structures that lie within the channel or the adjacent flood plain, as well as a low-flow navigational dam (Lock 

and Dam 4) approximately 0.8 mi downstream of station 

03287500. The City of Frankfort also has a Flood Protection 

System made up of levees, floodwalls, and pumping stations 

that protect Frankfort.

Previous Studies 

The FIS by FEMA is a compilation and presentation of 

flood risk within a community for the National Flood Insurance Program (NFIP) (Federal Emergency Management 

Agency, 2013). A FIS report is regulatory by nature and contains flood-elevation data in flood profiles and data tables that 

are based on theoretical flows. The flood inundation studies 

conducted by the USGS are non-regulatory by nature and contain detailed flood-elevation data in flood maps that are based 

on measured stages and (or) flows. 

 The current FIS for Franklin County (Federal Emergency Management Agency, 2007) was completed by the URS 

Corporation in April 2010. The FIS provided information on 

water-surface profiles and associated flood-plain maps for the 

Kentucky River at 1.0- and 0.2-percent annual exceedance 

probabilities. The City of Frankfort provided the hydraulic 

model used in the FIS, which contained bathymetric and structure datasets for most of the study area. 
Introduction 3

Figure 1. Location of study reach for the Kentucky River at Frankfort, Kentucky, and location of USGS streamgages. 

The National Weather Service forecast point (FFTK2) is at USGS streamgage Kentucky River at Lock 4 at Frankfort, Kentucky 

(station no. 03287500). 

!



03287500 §

%&'64

%&'%&'(64 64

(127

/

(127

(60

/

(60

/

(460

/

(421

Projection: Lambert Conformal Conic

State Plane Coordinate System, Kentucky, FIPS, 1600

North American Datum of 1983 (NAD83)

Orthophotography from Kentucky Aerial Photography 

and Elevation Data Program, 2012

Frankfort

Kentucky River

KENTUCKY

Study area

0 0.5 1 MILE

0 0.5 1 KILOMETER

84°55'

38°14'

84°54' 84°53' 84°52' 84°51' 84°50' 84°49'

38°13'

38°12'

38°11'

38°10'

Versailles

Road

East West Connector

B

Lock and Dam 4 enson Creek

EXPLANATION

03287500

!

§ USGS streamgage and number

Flow arrow—Indicates direction of 

 water flow

Centerline Kentucky River

Limits of study area

%&'64 (127 Route markers

!

§
4 Flood-Inundation Maps for a 6.5-Mile Reach of the Kentucky River at Frankfort, Kentucky

Constructing Water-Surface Profiles

The following steps were taken to construct the watersurface profiles: (1) examination of current and historical 

data from a streamgage on the Kentucky River (table 1); (2) 

collection of hydrologic and steady-flow data; (3) collection of 

topographic data, geometric data (for structures/bridges), and 

bathymetric data throughout the study reach; (4) determination 

of energy-loss factors (roughness coefficients) in the stream 

channel and flood plain; (5) model calibration and evaluation, and (6) computation of water-surface profiles by means 

of HEC–RAS, the U.S. Army Corps of Engineers’ hydraulic 

modeling software (U.S. Army Corps of Engineers, 2010).

The water-surface profiles used to produce the 26 

flood-inundation maps in this study were computed by using 

HEC–RAS, version 4.1.0 (U.S. Army Corps of Engineers, 

2010). HEC–RAS simulates the flow of water through open 

channels and computes water-surface profiles. HEC–RAS is 

a one-dimensional step-backwater model for simulation of 

water-surface profiles with steady-state (gradually varied) 

or unsteady-state flow computation options. The HEC–RAS 

analysis for this study was done by using the steady-state flow 

computation option.

Methods used are generally cited from previously 

published reports. If techniques varied significantly from 

previously documented methods because of local hydrologic 

conditions or available data, they are described in detail in 

this report. Maps were produced for water levels referenced 

to the water-surface elevation (stage) at station 03287500 

and ranging from near bankfull (27 ft; 488.58 ft above the 

North American Vertical Datum of 1988 (NAVD 88)) to the 

elevation that breaches the levees protecting Frankfort (52 ft; 

513.58 ft above NAVD 88). 

Hydrologic and Steady-Flow Data

The study-area hydrologic network consists of one USGS 

streamgage (fig. 1; table 1). The streamgage on Kentucky 

River at Lock 4 at Frankfort, Kentucky (station no. 03287500) 

has a continuous record of measured stage (water level) and 

computed streamflow (table 1). All measured stages and corresponding water-surface elevations are referenced to NAVD 88. 

The USGS streamgage within the study reach is equipped with 

satellite radio transmitters that allow data to be transmitted in 

near real time. Flow and stage data for a particular streamgage 

can be accessed online from the USGS at http://waterdata.

usgs.gov/ky/nwis/current/?type=flow.

Steady-flow data necessary for the hydraulic model 

consisted of flow regime, downstream boundary conditions (either known water-surface elevation associated with 

a discharge measurement, critical depth, normal depth, or 

streamgage rating-curve value), and peak-discharge information. The hydraulic model developed contains a normal depth 

boundary condition using an average channel slope within 

the study domain. The steady-flow data for the study reach 

were obtained from previous studies and field measurements 

of streamflow made at station 03287500, and the most current 

(2013) stage-discharge relation at station 03287500. 

Topographic/Bathymetric Data

Light Detection And Ranging (LiDAR) data near Frankfort were furnished by the Kentucky Energy and Environment 

Cabinet (Carey Johnson, Kentucky Energy and Environment 

Cabinet, written commun., 2012). LiDAR provides highresolution topographic data for models and other applications. 

The LiDAR data used in the study had a horizontal resolution of 5.0 ft and a vertical accuracy of 0.229 ft. The LiDAR 

data were collected and postprocessed by Photo Science, Inc. 

(Lexington, Kentucky), in 2012, resulting in a series of tiled 

bare-earth digital elevation models (DEMs). The DEM tiles 

that covered the study area were mosaicked together using 

geoprocessing tools in ArcGIS.

 River bathymetry data within the study reach were collected by the USGS Kentucky Water Science Center (Albert 

Ruby, USGS Kentucky Water Science Center, written commun., 2012). The bathymetric survey was run June 27–28, 

2012. A 210-kilohertz AirmarTM transducer and a Reson NavisoundTM 210 echo sounder were used to collect the bathymetric data. A Trimble TM Differential Global Positioning System 

(DGPS) was used for horizontal positioning during the survey. 

The HYPACK TM navigation software package was used to 

integrate riverbed depths along with the DGPS horizontal 

position data and to display the location of the boat on a georeferenced aerial photo of the river for navigation. 

A computer program was developed in Python (Python 

Software Foundation, 2013) to postprocess the raw bathymetric data and create a series of properly oriented cross sections 

that span the width of the river. By using the series of cross 

sections, a bathymetric surface was created with the inverse 

distance weighted interpolation routine in ArcGIS. The bathymetric surface was then merged with the bare-earth DEM. 

The Louisville District of the U.S. Army Corps of Engineers (James Lowe, U.S. Army Corps of Engineers, written 

commun., 2013) provided a levee dataset from February, 29, 

2008, containing surveyed elevations of the North and South 

Frankfort levees. The surveyed levee dataset was merged with 

the bare-earth DEM.

A total of six hydraulic structures exist within the study 

area and all were included in the hydraulic model. The structure datasets within the study area originated from the FIS for 

Franklin County (Federal Emergency Management Agency, 

2007) and included structure surveys of the Kentucky River 

within the mapped river reach (fig. 1). The structure datasets 

were checked and validated in consultation with the City of 

Frankfort (Deron Rambo, City of Frankfort at the Office of 

Emergency Management, written commun., 2013) to ensure 

that no newly built structures were within the study area. 
Constructing Water-Surface Profiles 5

HEC-GeoRAS and ArcGIS were used to extract flood 

plain elevations from the LiDAR-derived DEM at selected 

cross sections along the Kentucky River for use in the 

HEC–RAS model. The flood plain and river bathymetry 

elevations were merged with the structure datasets during the 

development of the HEC–RAS model. 

Energy-Loss Factors

USGS field observations and photographs, along with 

high-resolution aerial photographs furnished by the City of 

Frankfort (Kentucky GIS Server, 2013), were used to select 

initial (precalibration) channel and flood plain friction coefficients. These friction coefficients, commonly called Manning’s roughness coefficients or Manning’s n values, account 

for energy (friction) loss in model calculations. The final 

Manning’s n values used ranged from 0.04 to 0.043 for the 

main channel and 0.12 to 0.13 for the overbank areas; these 

values were selected according to the channel and flood plain 

characteristics described by Chow (1959). The main channel 

banks and overbank areas throughout the study area domain 

are highly vegetated. 

Model Calibration and Performance

The hydraulic model was calibrated to the most current 

stage-discharge relation at station 03287500 (Kentucky River 

at Lock 4 at Frankfort, Kentucky), using a total of 24 profiles. 

The hydraulic model was also calibrated to 19 high-watermark measurements collected for the flood event that occurred 

on May 5, 2010 (Albert Ruby, USGS Kentucky Water Science Center, written commun., 2010). Model calibration was 

Table 1. USGS streamgage information for study basin, Kentucky River, Kentucky.

[mi2, square miles; ft, feet; NAVD 88, North American Vertical Datum of 1988]

Station name Station 

number

Drainage area 

(mi2)

Latitude 

(degrees, 

minutes, 

seconds)

Longitude

(degrees, 

minutes, 

seconds)

Period of record

Maximum recorded 

stage at streamgage 

(ft above NAVD 88) 

and date

Kentucky River 

at Lock 4

03287500 5,411.0 38°12′06′′ N. 84°52′54′′ W. Oct. 1927 to current 

year (2013).

48.47 ft (510.05 ft )

December 10, 1978.

accomplished by adjusting Manning’s n values until the results 

of the hydraulic computations closely agreed with the known 

flood discharge and stage values; Manning’s n values were 

also verified to fall within realistic bounds, as described by 

Chow (1959). Differences between measured and simulated 

water levels for specified flows from the established stagedischarge relation were less than −0.34 ft (table 2). Differences 

between measured and simulated water levels for models 

calibrated to flood events were less than −0.83 ft (table 3). 

These calibration results demonstrate that the model is capable 

of simulating accurate water levels over a wide range of flows 

in the basin. 

Development of Water-Surface Profiles

Profiles were developed for 26 stages at 1-ft intervals 

between 27 ft and 52 ft as referenced to station 03287500. 

Discharges corresponding to the various stages were obtained 

from the most current stage-discharge relation (2013) at 

station 03287500 (Kentucky River at Lock 4 at Frankfort, 

Kentucky). 

Discharges for all profiles (table 4) were selected with 

the assumption that, within the 6.5-mi study reach, there are 

no significant inflows. The discharges were estimated to be 

uniform and steady throughout the study reach. The watersurface elevations and the corresponding discharge estimates 

used for stages 51.0 ft and 52.0 ft were obtained by using the 

fully calibrated model in an iterative approach with various 

flows. These stages correspond to the water levels that breach 

the North and South Frankfort levees. 
6 Flood-Inundation Maps for a 6.5-Mile Reach of the Kentucky River at Frankfort, Kentucky

High-watermark station 

(distance 

from most 

downstream 

cross section) 

(feet)

High-watermark 

elevation

(feet)

Model 

water-surface 

elevation

(feet)

Elevation 

difference

(model highwater mark)

(feet)

24,689.61 507.28 507.26 −0.02

22,287.00 507.00 506.91 −0.09

20,614.58 506.57 506.69 0.12

18,819.53 506.50 506.36 −0.14

18,819.53 506.53 506.36 −0.17

15,701.44 505.65 505.52 −0.13

14,661.57 505.11 505.28 0.17

13,825.44 504.61 505.10 0.49

13,101.34 505.42 505.15 −0.27

12,301.77 505.37 504.97 −0.40

11,201.91 504.96 504.78 −0.18

11,137.62 505.44 504.76 −0.68

9,760.12 504.75 504.35 −0.40

8,913.91 504.55 504.20 −0.35

8,634.60 504.63 504.17 −0.46

7,831.73 504.00 504.01 0.01

7,709.92 504.52 503.99 −0.53

5,607.48 504.42 503.67 −0.75

4,674.39 504.06 503.23 −0.83

Table 3. Comparison of hydraulic-model output and high water 

mark elevations for a major flood event on May 5, 2010, Kentucky 

River, Kentucky. Gage datum: 461.58 ft (NAVD 1988).

Rating 

stage 

(feet)

Rating 

elevation 

(feet)

Model 

water-surface 

elevation

(feet)

Elevation 

difference

(model rating)

(feet)

27.0 488.58 488.74 0.16

28.0 489.58 489.56 −0.02

29.0 490.58 490.35 −0.23

30.0 491.58 491.42 −0.16

31.0 492.58 492.27 −0.31

32.0 493.58 493.36 −0.22

33.0 494.58 494.24 −0.34

34.0 495.58 495.36 −0.22

35.0 496.58 496.51 −0.07

36.0 497.58 497.4 −0.18

37.0 498.58 498.57 −0.01

38.0 499.58 499.42 −0.16

39.0 500.58 500.62 0.04

40.0 501.58 501.53 −0.05

41.0 502.58 502.74 0.16

42.0 503.58 503.63 0.05

43.0 504.58 504.82 0.24

44.0 505.58 505.68 0.1

45.0 506.58 506.88 0.3

46.0 507.58 507.76 0.18

47.0 508.58 508.63 0.05

48.0 509.58 509.81 0.23

49.0 510.58 510.64 0.06

50.0 511.58 511.48 −0.1

Table 2. Comparison of hydraulic-model output and stagedischarge rating at Kentucky River at Lock 4 at Frankfort, 

Kentucky. 
Constructing Water-Surface Profiles 7

Table 4. Stages (elevations), in feet, with corresponding discharge estimates at USGS station 03287500 (Kentucky River at Lock 4 at 

Frankfort, Kentucky) for selected simulated water-surface profiles.

[NAVD 88, North American Vertical Datum of 1988]

Stage, in feet above gage datum (elevation, in feet, NAVD 88) 

associated with the indicated discharge value, in cubic feet per second

Stage (elevation) 27.00

(488.58)

28.00

(489.58)

29.00

(490.58)

30.00

(491.58)

31.00

(492.58)

32.00

(493.58)

33.00

(494.58)

34.00

(495.58)

35.00

(496.58)

36.00

(497.58)

Discharge 67,700 70,100 72,500 75,000 77,600 80,200 82,900 85,700 88,500 91,300

Map sheet no. 1 2 3 4 5 6 7 8 9 10

Stage (elevation) 37.00

(498.58)

38.00

(499.58)

39.00

(500.58)

40.00

(501.58)

41.00

(502.58)

42.00

(503.58)

43.00

(504.58)

44.00

(505.58)

45.00

(506.58)

46.00

(507.58)

Discharge 94,200 97,000 100,000 103,000 106,000 109,000 112,000 115,000 118,000 121,000

Map sheet no. 11 12 13 14 15 16 17 18 19 20

Stage (elevation)

47.00

(508.58)

48.00

(509.58)

49.00

(510.58)

50.00

(511.58)

51.00

(512.58)

52.00

(513.58)

Discharge 124,000 127,000 130,000 133,000 136,850 140,425

Map sheet no. 21 22 23 24 25 26
8 Flood-Inundation Maps for a 6.5-Mile Reach of the Kentucky River at Frankfort, Kentucky

Figure 3. Comparison of hydraulic-model output and high-water-mark elevations for a major flood 

event on May 5, 2010, Kentucky River, Kentucky. Gage datum—461.58 ft (NAVD 1988).

Figure 2. Comparison of hydraulic-model output and stage-discharge rating at Kentucky 

River at Lock 4 at Frankfort, Kentucky (USGS station no. 03287500).

Model points

Measured points

EXPLANATION

60

50

40

Stage, in feet

Discharge, in cubic feet per second

30

20

10

101 102 103 104 105

0

Channel elevation

Model water-surface elevation

High-water marks

EXPLANATION

Distance from most downstream cross section, in feet

420

0 5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000

540

520

500

480

Elevation, in feet

460

440
Inundation Mapping 9

Inundation Mapping

Flood-inundation maps were created for a river reach 

near Frankfort, Kentucky, referenced to a USGS streamgage 

site, station 03287500 (Kentucky River at Lock 4 at Frankfort, Kentucky), which is also an NWS flood-forecast point. 

The inundation maps were created in ArcGIS, a geographic 

information system, by combining the water-surface profiles 

from the hydraulic model and DEM data. The DEM data were 

derived from 5.0-ft-horizontal-resolution LiDAR data with a 

vertical accuracy of 0.229 ft, obtained from Photo Science, 

Inc. Estimated flood-inundation datasets for each simulated 

water-surface profile were developed with HEC–GeoRAS 

software (U.S. Army Corps of Engineers, 2009). HEC–GeoRAS is a set of procedures, tools, and utilities for processing 

geospatial data in ArcGIS by use of a graphical user interface. The interface allows the preparation of geometric data 

for import into HEC–RAS and processes simulation results 

exported from HEC–RAS (U.S. Army Corps of Engineers, 

2010). The datasets produced by using HEC-GeoRAS 

included flood-inundation polygons and water depth grids. 

The procedure used to create the datasets for each simulated 

water-surface profile included creating a bounding polygon 

that defined the analysis extent for mapping the inundation. 

Then, surfaces containing the water-surface elevation for 

each simulated water-surface profile were created within the 

analysis extent. Lastly, the DEM was subtracted from each 

surface containing the water-surface elevation for each simulated water-surface profile, resulting in the final water depth 

grids. The water depth grids were then converted to the final 

flood-inundation polygons representing the inundation extent. 

The HEC-GeoRAS results were modified to ensure a hydraulically reasonable transition of the boundary between modeled 

cross sections relative to the contour data for the land surface. 

The resulting inundation maps have a vertical accuracy of 

about 1.0 ft. The maps show estimated flood-inundated areas 

overlaid on high-resolution, georeferenced aerial photographs 

of the study area for each water-surface profile generated by 

the hydraulic model.

Kentucky River, Kentucky, Flood-Inundation 

Maps on the Internet

The flood-inundation maps and current study documentation are available online at the U.S. Geological Survey 

Publications Warehouse (http://dx.doi.org/10.3133/sim3278/). 

Also, a Flood Inundation Mapping Science Web site has been 

established to provide a portal for USGS flood-inundation 

study information to the public at http://water.usgs.gov/osw/

flood_inundation/. That Web portal has a link (http://wim.usgs.

gov/FIMI/FloodInundationMapper.html) to interactive online 

map libraries that can be downloaded in several commonly 

used electronic file formats. In the latter link, each stream 

reach displayed contains further links to NWISWeb graphs of 

the current stage and streamflow at USGS station 03287500 to 

which the inundation maps are referenced. A link also is provided to the NWS AHPS site (http:/water.weather.gov/ahps/) 

so that the user can obtain applicable information on forecasted peak stage. The estimated flood-inundation maps are 

displayed in sufficient detail to note the extent of flooding with 

respect to individual structures so that preparations for flooding and decisions for emergency response can be performed 

efficiently. Roadways and bridges were closely reviewed and 

are shown as shaded (inundated and likely impassable) or not 

shaded (dry and passable) to facilitate emergency planning and 

use. The policy set forth by the National Weather Service is 

that a bridge is considered to be inundated when the watersurface elevation exceeds the low chord (“low steel,” or low 

member) of the bridge. However, buildings that are shaded do 

not reflect inundation but denote that bare-earth surfaces in the 

vicinity of the buildings are inundated. When the water depth 

(as indicated in the Web Mapping Application by holding the 

cursor over an inundated area) in the vicinity of the building 

of interest exceeds that building’s height, the structure can be 

considered fully submerged.

Disclaimer for Flood-Inundation Maps

Inundated areas shown should not be used for navigation, 

regulatory, permitting, or other legal purposes. The USGS 

provides these maps “as-is” for a quick reference, emergency 

planning tool but assumes no legal liability or responsibility 

resulting from the use of this information.

Uncertainties and Limitations for Use of FloodInundation Maps 

Although the flood-inundation maps represent the boundaries of inundated areas with a distinct line, some uncertainty 

is associated with these maps. The flood boundaries shown 

were estimated on the basis of stages (water-surface elevations) and streamflows at selected USGS streamgages. Watersurface elevations along the stream reaches were estimated by 

steady-state hydraulic modeling, assuming unobstructed flow, 

and using streamflows and hydrologic conditions anticipated 

at the USGS streamgage. The hydraulic model reflects the 

land-cover characteristics and any bridge, dam, levee, or other 

hydraulic structures existing as of June 2013. Unique meteorological factors (timing and distribution of precipitation) may 

cause actual streamflows along the modeled reach to vary 

from those assumed during a flood, which may lead to deviations in the water-surface elevations and inundation boundaries shown. Additional areas may be flooded due to unanticipated conditions such as changes in the streambed elevation 

or roughness, backwater into small tributaries along the study 

reach, or backwater from localized debris or ice jams. The 

accuracy of the floodwater extent portrayed on these maps will 

vary with the accuracy of the digital elevation model used to 

simulate the land surface. 
10 Flood-Inundation Maps for a 6.5-Mile Reach of the Kentucky River at Frankfort, Kentucky

If this series of flood-inundation maps will be used in 

conjunction with NWS river forecasts, the user should be 

aware of additional uncertainties that may be inherent or factored into NWS forecast procedures. The NWS uses forecast 

models to estimate the quantity and timing of water flowing 

through selected stream reaches in the United States. These 

forecast models (1) estimate the amount of runoff generated 

by precipitation and snowmelt, (2) simulate the movement of 

floodwater as it proceeds downstream, and (3) predict the flow 

and stage (water-surface elevation) for the stream at a given 

location (AHPS forecast point) throughout the forecast period 

(every 6 hours and 3 to 5 days out in many locations). For 

more information on AHPS forecasts, please see http://water.

weather.gov/ahps/pcpn_and_river_forecasting.pdf. 

Summary

A series of estimated flood-inundation maps were 

developed in cooperation with the City of Frankfort Office of 

Emergency Management for the Kentucky River at Frankfort, 

Kentucky. These maps, available through a USGS Web portal, 

in conjunction with the real-time stage data from the USGS 

streamgage 03287500 (Kentucky River at Lock 4 at Frankfort, 

Kentucky) and National Weather Service flood-stage forecasts, will help to guide the general public in taking individual 

safety precautions and will provide city officials with a tool 

to efficiently manage emergency flood operations and flood 

mitigation efforts. 

The maps were developed by using the U.S. Army Corps 

of Engineers’ HEC–RAS and HEC-GeoRAS programs to 

compute water-surface profiles and to delineate estimated 

flood-inundation areas for selected stream stages. The maps 

show estimated flood-inundation areas overlaid on highresolution, georeferenced aerial photographs of the study area 

for stream stages between 27 ft and 52 ft at station 03287500. 

The maps are available at the USGS Web portal at http://

dx.doi.org/10.3133/sim3278/ and at the USGS Flood Inundation Mapping Science Web site at http://wim.usgs.gov/FIMI/

FloodInundationMapper.html, where users can interact with 

the maps and gain a general indication of depth of water at any 

point. 

References Cited

Chow, V.T., 1959, Open-channel hydraulics: New York, 

McGraw-Hill, 680 p.

Federal Emergency Management Agency, 2007, Flood insurance study for Franklin County, Kentucky: Washington 

D.C., Flood Insurance Study 21073CV000B.

Federal Emergency Management Agency, 2013, Flood insurance study Web page, accessed August 28, 2013, at 

http://www.fema.gov/floodplain-management/floodinsurance-study.

Python Software Foundation, 2013, Python programming language, accessed August 28, 2013, at http://www.python.org/.

U.S. Army Corps of Engineers, Hydrologic Engineering 

Center, 2009, HEC-GeoRAS, GIS tools for support of 

HEC–RAS using ArcGIS—User’s manual, version 4.2 

[variously paged].

U.S. Army Corps of Engineers, Hydrologic Engineering 

Center, 2010, HEC–RAS River Analysis System—

Hydraulic Reference Manual, version 4.1 [variously paged]. 

U.S. Census Bureau, 2012, 2012 Census interactive population 

search, KY—Frankfort town: Washington, D.C., accessed 

August 28, 2013, at http://quickfacts.census.gov/qfd/

states/21/2128900.html.

Glossary

Annual exceedance probability The probability that a particular flood size will occur in any given year. As an example, 

a 1-percent annual exceedance probability flood has a 1-percent chance of being equaled or exceeded in any single year. A 

1-percent annual exceedance probability flood is also referred 

to as a “100-year flood.”

DEM Digital elevation model (DEM), a digital file consisting 

of terrain elevations for ground positions at regularly spaced 

horizontal intervals.

Depth grid A digital file consisting of the mathematical difference between the water-elevation surface and ground-elevation surface for ground positions at regularly spaced horizontal 

intervals.

Gage height Term used by the USGS National Water Information System display to describe the height of water above 

the datum at a streamgage. It is synonymous with stage.

Inundation surfaces Surfaces representing areas covered 

by water, derived as the mathematical difference between the 

water-elevation surface and ground-elevation surface.

Rating curve The relation between stage and discharge at a 

cross section in a river. 

Stage Term used by the National Weather Service to 

describe the height of water above the datum at a streamgage. 

It is synonymous with gage height. 

Water-surface elevation Elevation of water at a streamgage 

determined by adding the gage height of the water to the 

datum for the streamgage. 

Water-surface profile A diagram showing how the elevation 

of a river changes along its centerline.

Lant— Flood-Inundation Maps for a 6.5-Mile Reach of the Kentucky River at Frankfort, Kentucky —Scientific Investigations Map 3278

ISSN 2329-132X (online)

http://dx.doi.org/10.3133/sim3278